Tuning Guide

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Uprating a classic is worthwhile yet many do it wrongly! So before you get cracking, decide what you want… and how to achieve it

Now that the DfT (one letter short of daft?) has done a U-turn on its unworkable modified rules concerning MoT exemption, we can all tune and tweak freely – yet should we? Like cooking, the proof of the pudding is in the eating and it’s easy to get the ingredients’ mix wrong, eating up your time, effort and least of all your hard earned money.

If it’s any consolation, you wouldn’t be the first or last but in this Road & Track special we hope to put on the right road to get the best from your classic for the least outlay.

Power gains

On the face of it, this appears to be the easiest type of upgrades because enthusiasts have been devising and developing tweaks for decades and before the Mini came along. And yet it is here where the majority of mistakes are made, essentially by putting too much emphasis on the hallowed 0-60mph times. Admittedly, they are a industry respected indication but it’s a brutal affair to achieve these figures (ask our Stuart Bladon!) and your prized classic wouldn’t last long driven constantly in such a manner.

Of far more importance, for real world motoring, is the 30-70mph times through the gears and to achieve the quickest requires a different tuning approach that depends on your driving style. For instance, if you’re the type who likes to use maximum revs and wield the gear lever like Federer does his racket, then opt for a fairly wild tune using a big-valved head and a racier camshaft. However, the downside is invariably loss of low speed torque which means in normal driving your classic will probably perform worse than standard until the engine comes ‘on cam’.

A sportier performance camshaft will give more power but at the expense of low speed pulling torque (as in the case of the MGB). Also, while it’s one of the less expensive go-faster components the camshaft is only worth changing after you have uprated the carb and perhaps the cylinder head or the engine will perform worse than standard.

Proof of this came from a weekly back in the 70s when it tested three Capris; a 1300GT, a 1600XL and the 1600GT. Now the 1300GT and regular 1600 both delivered 72bhp but very differently. In full revs mode they were quite evenly matched, but in third and top gear acceleration from 30mph the standard 1600 was by far the quickest and even beat the 1600GT (partly due to the latter’s higher gearing) until up to 60mph. In other words, if you demand a snappier performance but without driver effort refrain from going overboard on the engine tune.

A single twin choke is as effective and easier to keep in tune than multiple carbs which require careful balancing so they work in unison. Fitting a standard but larger carb from a sportier or bigger-engined version of your classic can give a useful power increase plus retain standard looks and air filter assemblies.

It was usually seen as the Right Thing to dump the standard air filter in favour of sexy chrome ‘pancake’ types. However, while they look and sound the part their effectiveness is in doubt over the stock item. Much better are today’s freer-flowing foam or cotton types from the likes of K&N and Pipercross which work plus if you want to keep the engine’s appearance standard there’s also similar filter elements which fit in the standard air filter assembly.

Exhausts are popular and there’s usually a sports manifold and system for the majority of classics. Apart from expelling the gasses, a good exhaust also helps ‘pull’ in the new mixture by way of scavenging. On many classics, a enhanced manifold and system gives a good 10 per cent power gain on its own but if you intend to keep the engine in stock tune as too wild a system may affect the fuelling and impair performance rather than improve it.

A superior cylinder head is the way to get ahead as this is where the combustion process takes place and most oldies suffer from poor designs and finishing, areas which were only really improved in the ’80s.

Most classics are best tuned in this manner. Generally, there’s three states of tune ranging from a simple clean up and re-profiling of the standard machining and perhaps a higher compression ratio (the valve sizes remain standard) to a full on re-engineering of the head boasting the largest valve sizes and compression ratio possible; this is mainly for competition work. Mid way ‘Stage 2’ is perhaps the best compromise for most owners as it will improve power right across the rev range.

Many enthusiasts overlook the ignition because it’s not so much how much power you can gain here but to reduce how much you may be losing due to wear. Electronic ignition is a worthy fitment even if you’re not after extra power as it ensures it can’t go out of tune, although for improved power you should look at a sports distributor at the same time if other tuning mods are planned.

Running gear

Most classics can be usefully updated in this department if for no other reason that age and mileage will have caused gradual deterioration that can go unnoticed. What’s more, uprated replacements cost much the same as originals – cheaper if aftermarket types, although are not usually exactly to the original spec due to their universal fit nature plus can be appreciably stiffer by design to account for ‘relaxing’ of the chassis.

Now the bad news – it’s easy to mess things up here by using a mix of parts totally unsuited to each other. You may not think so by the way certain oldies handle but vehicle manufacturers go to a lot of time and effort to achieve a fair compromise, while on prestige cars, such as Lotuses and Porsches, it can be difficult to improve on the standard spec.

Harder springs are readily available improve the handling and can reduce roll but make the ride harsher. A harder setting at the rear can also reduce understeer if it’s excessive due to roll stiffness but you ideally must combine any spring change with new appropriate dampers as there will be a mis-match.

Lowering also reduces roll by lowering centre of gravity but spoils originality and usually impairs ride – it’s folly to think that racing springs are ultimate for the road for the same reason.

Anti roll bars and compliance bushes do what they say on the tin and are there to add stiffness to the chassis and reduce roll. Available for most classics in various thicknesses but you need to speak to a specialist on what’s best for you as they need to be matched to the rest of the mods because they dictate under and oversteer. Replacing standard bushes with ‘poly’ types is popular if for no other reason that they last longer as well as provide added tautness to the chassis but, again, speak to a marque expert first as it’s easy to overdo it and make the car too harsh as a result.

Brakes

What oldie doesn’t benefit from better brakes, even if for peace of mind – although do you need them? Unless you drive particularly hard or are experiencing poor performance or fade, installing harder pads or linings can have a negative effect as they will not reach optimum working temperature unless worked harder. If anything, a mild upgrade along the lines of EBC GreenStuff pads may be all that’s required and some experts still regard the original asbestos type linings superior in performance.

Most people think that you have to convert classic with all drum brakes to front discs if you want better stopping power. Not so! Drum brakes can work perfectly well if they are maintained right and are shod with quality linings (uprated types are available). Unless you intend to drive hard, constantly, where fade may become a problem, a drum brake is quite acceptable plus they also posses a ‘servo effect’ easing pedal pressure.

MGA expert Bob West is a lover of their drum brakes and sees no reason to convert to discs in many cases, where conversions usually include a servo to reduce pedal pressure. Also, yet often overlooked, fitting front discs to an all drum system can lead to brake imbalance on some classics that requires different rear wheel cylinders or even the appropriate master cylinder also fitted. Speak to a marque expert or Owners’ Club if in any doubt.

If your car has disc brakes already fitted then apart from harder brake pads, you also have the option of fitting larger discs, to give a larger brake pad area to work with along with beefier callipers that exert more force on the disc and ease pressure at the pedal although this is usually only necessary after large-scale power gains or you envisage track work. Aftermarket types have the option of normal or ventilated types, some featuring special drilled holes or grooves. Rear discs can also be fitted, although as around 65 per cent of braking is done by the front brakes, it’s usually quite unnecessary for road use.

Before laying out good money on aftermarket kits, check to see if a larger disc or calliper was also fitted to your car, either due to being a sportier version or having larger engines in the range. When they may be of benefit is modern brake pipes, which are stronger and give the pedal more feel, highlighted if old ones are past their prime.

Get the basics right first

Before any modifying to the suspension is contemplated you have to ensure that your car is in A1 condition beforehand as you’ll be wasting your time and money. Ok, you were going to replace the dampers anyway, but what about the king pins, wheel bearings, and so on? And have the geometry set up by a marque expert – it can make all the difference, as many Triumph TR6 and Jaguar XK owners will verify. Seasoned journalist and (Le Mans) racer of note, Tony Dron, road tested MGBs when contemporary and now feels, looking back, that the trouble with many standard cars remains that they are simply incorrectly set up. In his experience, Dron feels MGBs are particularly sensitive to rear ride heights and the steering geometry. Along with the right anti-roll bar he believes, “Get those things sorted and any MGB will steer and corner beautifully.” Furthermore, he wondered, why so many MGB road cars he’s driven over the decades don’t and, crucially, why their owners are oblivious to this cheap tweak. “It strikes me that many owners are missing out…. it costs nothing to make a standard MGB handle brilliantly…. and getting it right has nothing to do with buying special parts,” he wrote in Octane a while back.

Motor, said of a ‘Stage 2 Midget’ that also sported a properly developed stiffer lower suspension yet standard roll bar: “Like the standard car, it understeers gently but there is plenty in reserve to kick the tail out or the nose will tuck in on a trailing throttle. So, however you drive, it’s quick, safe and very controllable”.

On a roll

Before carrying out any tuning it’s essential that the engine is fit enough so have a compression test carried out first. A thorough rolling road ‘dyno’ tune can release a lot of hidden power, even on a standard engine, simply by carefully discovering the right ignition timing and fuelling for your particular unit as tolerances did vary considerably during the 1960s and 70s. It may yield all the added power you demand yet also be completely standard at the same time.

Getting in the right gear

Most classics are too low geared for today’s roads and why fitting modern five-speed gearboxes has become so popular that it’s now an accepted mod across the board. However, while the extra ratio aids cruising, it has to be tailored to the engine’s power, which if too low will be counter productive as the car will never be able to ‘pull’ the higher gear. For example, on Morris Minors, it only works efficiently if the engine has been tuned to say around 80bhp+ to cope. If you wish to keep the car standard, consider raising the gearing by fitting larger tyres or a higher axle ratio instead. Also, unless you are tuning the engine with a wider ‘rev band’, don’t think that a closer ratio gearbox from a GT version of your classic will help simply on its own – it can usually makes matters worse!